An electromagnetically controlled fuel injection valve is used for a pressure-accumulating type fuel injection apparatus such as a common rail. The fuel injection valve injects high-pressure fuel, which is fed from the common rail, into a combustion chamber of an engine. The fuel injection valve includes an injection valve body having an injection nozzle and a solenoid valve. The solenoid valve includes a solenoid and a valve device. The solenoid receives a control signal from an engine control unit (ECU), so that the solenoid opens and closes the valve device. The valve device controls pressure of fuel received in a pressure control chamber that actuates the injection valve body.
The solenoid has a movable member that is axially displaced when the solenoid is turned ON (energized) and the solenoid is turned OFF (de-energized). The movable member is used as a valve body of the valve device. The movable member is displaced, so that a valve port, which is an outlet port such as an orifice provided to the pressure control chamber, is opened. The outlet port is opened, so that hydraulic pressure of high-pressure fuel received in the pressure control chamber is controlled. Pressure is applied to a needle valve of the injection nozzle via a control piston of the valve body of the fuel injection valve, so that the control piston and the needle valve are displaced, and an injection nozzle port is opened and closed.
As shown in FIG. 2, a fuel injection valve 1 has a solenoid valve 3 that includes a solenoid 30 having an inner cylinder 32. The inner cylinder 32 radially internally receives a magnet core 33 that receives a magnet coil 35. The outer circumferential periphery of the magnet core 33 is surrounded by an outer cylinder 34. A movable member 5, which includes a flat-plate portion 51 and a shaft portion 52, are received in a lower portion of the magnet core 33. The flat-plate portion 51 has an attracted face on its upper side. The shaft portion 52 downwardly extends from the center of the flat-plate portion 51. The movable member 5 is supported by a cylindrical movable member holder 6 such that the shaft portion 52 is capable of vertically sliding in the movable member holder 6.
An orifice plate 7, which has an outlet orifice 73, is provided to the lower side of the movable member holder 6. A ball valve 78 is provided to the lower end of the shaft portion 52 to plug and unplug the outlet orifice 73. The movable member 5 is urged by a spring (biasing means) 36 to the lower side in the direction, in which the ball valve 78 plugs the outlet orifice 73. The movable member 5 is upwardly attracted in the direction, in which the ball valve 78 unplugs the outlet orifice 73, by magnetic force generated by the solenoid 30, so that the movable member 5 vertically displaces within a movable stroke that is about 0.05 mm. Response of displacement of the movable member corresponds to response of injection control of the fuel injection valve 1.
As the movable member 5 vertically displaces, the movable member 5 upwardly collides against a stopper face (lower end face) of the inner cylinder 32 and downwardly collides against the orifice plate 7 via the ball valve 78. Accordingly, the movable member 5 is repeatedly impacted.
Low-pressure fuel is filled in the solenoid. Therefore, when the movable member 5 vertically displaces, fluid resistance is generated due to viscosity of the low-pressure fuel. Therefore, fluid resistance of low-pressure fuel needs to be reduced for enhancing response of the movable member 5. Conventionally, multiple notches 53 shown in FIG. 5 are formed in the outer circumferential periphery of the movable member 50, so that fluid resistance of low-pressure fuel applied to the movable member 50 is reduced. Besides, weight of the movable member 5 is reduced by forming the notches 53. Thus, response of displacement of the movable member 50 is enhanced, so that response of injection control of the fuel injection valve 1 is enhanced.
A conventional movable member 5J shown on the left side in FIG. 6 has three notches 53 in the outer circumferential periphery of the flat-plate portion 51. Each notch 53 has a V-shape that circumferentially opens at a substantially 60° angle. Radial distance between a deepest portion 5A, i.e., smallest diameter portion of the flat-plate portion 51 and a contacting portion (contacting face 5D) is 0.9 mm. Oil passage grooves 58 are formed on an attracted face of the flat-plate portion 51 such that the oil passage grooves 58 communicate with the deepest portions 5A of the notches 53. Thus, low-pressure fuel can smoothly flow into the upper side of the flat-plate portion 51. Besides, weight of the movable member 5J can be reduced. However, stress is concentrated to the deepest portions 5A in the conventional movable member 5J due to impact arising in the vertical displacement. Therefore, the conventional structure of the movable member 5J does not have sufficient endurance.
A movable member 5H shown on the middle side in FIG. 6 has three notches 53, which have the same area as that of the conventional movable member 5J. Each notch 53 has a V-shape that circumferentially opens at a substantially 90° angle. Radial distance between a deepest portion 5A of the flat-plate portion 51 and the contacting face is 2.0 mm. In this structure, stress concentrated to the deepest portion 5A can be reduced compared with the structure of the conventional movable member 5J. However, each oil passage groove 58 communicates with the deepest portion 5A, and stress is apt to be concentrated to the deepest portion 5A. Accordingly, structural strength may be decreased, and endurance of the movable member 5H is not sufficiently enhanced.